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2024 AS Structured S1

Biology Quiz: Find the Incorrect Statement

Biology Quiz: Find the Incorrect Statement

Read each question and the statements below it. Click on the ONE statement you believe is INCORRECT. If you choose correctly, the reason why it’s wrong will appear, and you’ll earn a point.

Score: 0

State the typical approximate thickness of a cell surface membrane, including the appropriate unit.

Click the INCORRECT statement:
  • 1. The typical approximate thickness is 7 nm.
  • 2. The unit (nm) is essential.
  • 3. The acceptable range is 5 mm to 10 mm.
Reason Incorrect (#3): The acceptable range for cell surface membrane thickness is typically 5 nm to 10 nm. Millimeters (mm) represent a vastly larger scale and are incorrect for describing membrane thickness at this level.

Describe the primary function of each of the following components commonly found in a cell surface membrane: channel protein, phospholipid, glycoprotein, glycolipid, and cholesterol.

Click the INCORRECT statement:
  • 1. Channel protein: Facilitated diffusion, transport of specific substances (water, ions, water-soluble/polar molecules) down gradient.
  • 2. Phospholipid: Forms bilayer; barrier to water-soluble/polar substances; allows passage of lipid-soluble/non-polar substances; contributes to fluidity/stability.
  • 3. Glycoprotein: Acts as a receptor for cell signalling; involved in cell recognition and adhesion; primarily synthesizes ATP.
  • 4. Glycolipid: Acts as a receptor for cell signalling; involved in cell recognition (e.g., ABO antigens) and adhesion.
  • 5. Cholesterol: Regulates membrane fluidity (restricts movement high temp, disrupts packing low temp); reduces permeability to water-soluble substances.
Reason Incorrect (#3): Glycoproteins function as receptors for cell signalling and are involved in cell recognition and adhesion. ATP synthesis is the primary function of mitochondria, not glycoproteins.

Describe the key structural features of a mitochondrion, rough endoplasmic reticulum, and smooth endoplasmic reticulum as they would typically appear in a transmission electron micrograph.

Click the INCORRECT statement:
  • 1. Mitochondrion: Shows an outer membrane and a folded inner membrane forming cristae. Located within the cytoplasm.
  • 2. Rough Endoplasmic Reticulum (RER): Shows interconnected flattened sacs (cisternae) with ribosomes depicted as dots attached to the outer surface. Found outside the cell.
  • 3. Smooth Endoplasmic Reticulum (SER): Shows a network of tubules, lacking ribosomes on its surface. Can be shown connected to the RER or nuclear envelope. Located within the cytoplasm.
Reason Incorrect (#2): The Rough Endoplasmic Reticulum (RER) is located within the cytoplasm of eukaryotic cells. It is not found outside the cell.

Identify the organelle primarily responsible for modifying, sorting, and packaging proteins and lipids synthesized in the ER for secretion or delivery to other organelles. State one specific function of this organelle.

Click the INCORRECT statement regarding the Golgi:
  • 1. Name: Golgi body / Golgi apparatus / Golgi complex / dictyosome.
  • 2. Function: Modifies, sorts, and packages proteins and lipids synthesized in the ER for secretion or delivery to other organelles.
  • 3. Specific Function: Synthesizing lipids and steroids.
Reason Incorrect (#3): The Golgi apparatus modifies proteins (e.g., glycosylation), forms lysosomes, and helps produce plant cell wall components. Large-scale lipid and steroid synthesis is primarily a function of the Smooth Endoplasmic Reticulum (SER).

Explain how specific properties of water (such as its polarity, thermal properties, and state) contribute to its suitability as the primary component and transport medium of mammalian blood.

Click the LEAST relevant or INCORRECT statement:
  • 1. Excellent Solvent: Water’s polarity allows it to dissolve a wide range of ionic and polar substances, enabling transport.
  • 2. Transport Medium: Being a liquid, water acts as the medium for cell suspension and transport of dissolved substances.
  • 3. High Specific Heat Capacity: Water can absorb a large amount of heat with only a small rise in temperature, helping buffer body temperature.
  • 4. Low Density: Water’s low density allows blood to flow easily through narrow capillaries.
Reason Incorrect/Less Relevant (#4): Key properties making water suitable for blood include its role as a solvent (polarity), a transport medium (liquid state), and its ability to buffer temperature (high specific heat capacity). While density is a property of water, it is not typically highlighted as a primary reason for its suitability in blood function compared to the others; viscosity and pressure gradients are more direct factors in flow.

Name the major artery carrying oxygenated blood from the left ventricle to the systemic circulation and the major vein returning deoxygenated blood from the systemic circulation to the right atrium. Describe the primary function of each of these vessels.

Click the INCORRECT statement:
  • 1. Major Artery Name: Aorta.
  • 2. Aorta Function: Carries oxygenated blood under high pressure from the left ventricle to the systemic circulation.
  • 3. Major Vein Name: Vena cava.
  • 4. Vena Cava Function: Carries deoxygenated blood under high pressure from the systemic circulation back to the right atrium.
Reason Incorrect (#4): The Vena Cava carries deoxygenated blood from the systemic circulation back to the heart under low pressure, characteristic of large veins returning blood to the atria.

Explain the terms ‘closed’ and ‘double’ in the context of mammalian circulation, detailing why this circulatory system is described in this manner and outlining the two main circuits involved.

Click the INCORRECT statement:
  • 1. Closed: The blood is always contained within a continuous network of vessels.
  • 2. Double: The blood passes through the heart twice during one complete circuit.
  • 3. Pulmonary Circuit: Blood pumped from right heart to lungs and returns to left heart.
  • 4. Systemic Circuit: Blood pumped from right heart to body tissues and returns to left heart.
Reason Incorrect (#4): The Systemic Circuit begins when oxygenated blood is pumped from the left side of the heart to the body tissues; deoxygenated blood then returns to the right side of the heart.

Explain the physiological importance of the significant decrease in blood pressure as blood flows through arterioles before entering capillary networks.

Click the INCORRECT statement:
  • 1. Capillary Protection: Capillaries have very thin walls that are fragile. The lower pressure prevents them from being damaged or bursting.
  • 2. Efficient Exchange: The reduced pressure speeds up blood flow through the capillaries, allowing sufficient time for effective exchange.
  • 3. Fluid Balance: Lower pressure towards the venous end of the capillary bed facilitates the reabsorption of tissue fluid back into the capillaries.
Reason Incorrect (#2): The reduced blood pressure in arterioles leads to slower blood flow through the subsequent capillaries (due to increased total cross-sectional area and resistance). This slower flow provides adequate time for the efficient exchange of gases, nutrients, and waste products between the blood and tissues.

Compare and contrast the typical histological structure of a muscular artery with that of an arteriole, referencing differences in overall diameter, wall thickness relative to lumen size, and the composition (especially smooth muscle and elastic tissue) of their layers (tunica intima, media, and externa).

Click the INCORRECT statement:
  • 1. Similarities: Both have an innermost lining of endothelial cells (tunica intima); Both have a layer of smooth muscle (tunica media).
  • 2. Differences (Muscular Artery vs. Arteriole): Overall Size & Wall Thickness: Muscular arteries are smaller in diameter and have thinner walls relative to their lumen size compared to arterioles.
  • 3. Lumen: Muscular arteries generally have a wider lumen than arterioles (though arterioles can constrict significantly).
  • 4. Tunica Media: Muscular arteries have a much thicker tunica media with more layers of smooth muscle.
  • 5. Elastic Tissue: Muscular arteries have prominent internal and external elastic laminae and more elastic fibres within the tunica media compared to arterioles, which have less elastic tissue.
  • 6. Tunica Externa: Muscular arteries have a thicker, more defined outer layer of connective tissue (tunica externa/adventitia) than arterioles.
Reason Incorrect (#2): Muscular arteries are significantly larger in overall diameter and have considerably thicker walls relative to their lumen size when compared to the smaller arterioles.

For each of the following pathogens, state the major disease it causes and its typical mode(s) of transmission: Plasmodium species, Vibrio cholerae, Mycobacterium tuberculosis, and Human Immunodeficiency Virus (HIV). Also, indicate whether each pathogen is a prokaryote, eukaryote, or virus.

Click the INCORRECT statement:
  • 1. HIV: Virus; Disease: HIV/AIDS; Transmission: Body fluids.
  • 2. Plasmodium species: Eukaryote (Protist); Disease: Malaria; Transmission: Faecal-oral route.
  • 3. Vibrio cholerae: Prokaryote (Bacterium); Disease: Cholera; Transmission: Faecal-oral route.
  • 4. Mycobacterium tuberculosis: Prokaryote (Bacterium); Disease: Tuberculosis; Transmission: Airborne droplets / Aerosol infection.
Reason Incorrect (#2): Plasmodium species, the eukaryotic protists that cause malaria, are transmitted through the bite of an infected female Anopheles mosquito (vector transmission), not via the faecal-oral route.

Tenofovir is an antiretroviral drug effective against HIV. After phosphorylation within the host cell, its structure resembles deoxyadenosine monophosphate but crucially lacks the 3′-hydroxyl (-OH) group normally present on the deoxyribose sugar. Explain the mechanism by which tenofovir inhibits the action of HIV’s reverse transcriptase enzyme.

Click the INCORRECT statement describing Tenofovir’s mechanism:
  • 1. Competitive Inhibition: Tenofovir (phosphorylated) structurally resembles the natural substrate (dATP) and competes for the active site of HIV reverse transcriptase.
  • 2. Non-Competitive Inhibition: Tenofovir binds to an allosteric site on the enzyme, changing the active site shape.
  • 3. Chain Termination: When incorporated into the growing viral DNA strand, synthesis halts because tenofovir lacks the necessary 3′-hydroxyl (-OH) group required for forming the phosphodiester bond with the next nucleotide, thus preventing chain elongation.
Reason Incorrect (#2): Tenofovir functions as a competitive inhibitor because its structure mimics the natural substrate (dATP), allowing it to bind to the active site of reverse transcriptase. It also acts as a chain terminator. Binding to a separate (allosteric) site is characteristic of non-competitive inhibition, which is not Tenofovir’s primary mechanism described here.

In 2019, approximately 605,000 people globally received Pre-Exposure Prophylaxis (PrEP) for HIV prevention. A United Nations target set in 2016 aimed for 3,000,000 people to receive PrEP. Calculate the number of people who received PrEP in 2019 as a percentage of this UN target. Provide your answer rounded to the nearest whole number.

Click the INCORRECT calculation/answer:
  • 1. Calculation: (605,000 / 3,000,000) * 100% = 20.166…%
  • 2. Answer (nearest whole number): 21%
Reason Incorrect (#2): The calculation (605,000 / 3,000,000) * 100% results in 20.166…%. When rounded to the nearest whole number, this value is 20%.

Describe four distinct public health strategies that authorities can implement to reduce the transmission rates of HIV, explaining the mechanism by which each strategy contributes to prevention.

Click the INCORRECT or INAPPROPRIATE strategy for HIV:
  • 1. Promote Condom Use: Provide/educate on correct use. Explanation: Physical barrier preventing infected fluid exchange.
  • 2. Needle Exchange Programs: Provide sterile needles to IV drug users. Explanation: Reduces sharing of contaminated needles.
  • 3. Screening Blood Donations: Test donated blood/products. Explanation: Prevents transmission via transfusions.
  • 4. Antibiotic Therapy: Treat people with HIV using antibiotics. Explanation: Kills the virus directly.
Reason Incorrect (#4): HIV is a virus and is treated with antiretroviral drugs. Antibiotics are effective against bacterial infections, not viruses, and therefore are not used to treat HIV infection itself.

Identify the two main specialized cell types forming the epithelial lining of the larger airways (e.g., trachea, bronchi) in the mammalian gas exchange system, noting their key structural features (e.g., surface projections, secretory function).

Click the cell type NOT typically considered one of the two MAIN specialized epithelial lining cells:
  • 1. Cell with projections: Ciliated epithelial cell.
  • 2. Secretory cell: Goblet cell.
  • 3. Structural cell: Fibroblast.
Reason Incorrect (#3): The main specialized cells forming the epithelial lining of the large airways are ciliated epithelial cells (with surface projections for moving mucus) and goblet cells (which secrete mucus). Fibroblasts are connective tissue cells found deeper within the airway wall structure, not part of the primary epithelial lining itself.

Describe how the structure and coordinated action of the cells forming the pseudostratified ciliated columnar epithelium, including mucus production, contribute to the protection of the lungs from inhaled particles and pathogens.

Click the INCORRECT statement about the mucociliary escalator:
  • 1. Mucus Secretion: Goblet cells produce and secrete mucus.
  • 2. Trapping Debris: Sticky mucus traps inhaled particles (dust, pathogens).
  • 3. Mucociliary Escalator: Cilia on ciliated epithelial cells beat downwards, propelling mucus deeper into the lungs for disposal.
Reason Incorrect (#3): The cilia in the respiratory epithelium beat in a coordinated upward direction (towards the pharynx), moving the mucus layer with trapped debris out of the lower airways to be swallowed or expelled. This mechanism clears particles, it doesn’t propel them deeper into the lungs.

Describe the characteristic internal arrangement of microtubules, often referred to as the “9 + 2” array, that is observed in a transmission electron micrograph showing a cross-section of a eukaryotic cilium or flagellum.

Click the INCORRECT statement describing the “9 + 2” array:
  • 1. The cross-section shows: Nine pairs (doublets) of microtubules arranged in a peripheral ring.
  • 2. There are nine single microtubules located in the center.
  • 3. Associated proteins like dynein arms may also be mentioned/visible.
Reason Incorrect (#2): The characteristic “9 + 2” array found in eukaryotic cilia and flagella consists of nine outer microtubule doublets arranged in a ring around two central single microtubules, not nine central microtubules.

Explain which structural feature definitively shows that a cilium, despite projecting outwards, is fundamentally an extension of the cell’s cytoplasm and therefore an intracellular structure.

Click the INCORRECT explanation:
  • 1. The entire “9 + 2” microtubule structure of the cilium is enclosed within an extension of the cell surface membrane.
  • 2. This shows it’s an outgrowth containing cytoplasm.
  • 3. The cilium is attached directly to the nuclear envelope.
Reason Incorrect (#3): The fact that the entire internal structure (axoneme) of the cilium is enclosed by an extension of the cell’s own plasma membrane demonstrates that it is an outgrowth containing cytoplasm and is thus intracellular. While anchored by a basal body near the cell surface, it is not directly attached to the nuclear envelope.

Describe the primary functions of centrioles within an animal cell. Explain their specific roles and behavior during the different phases of the mitotic cell cycle, such as in a dividing stem cell.

Click the INCORRECT statement regarding centriole function/behavior:
  • 1. Function: Component of the centrosome (main Microtubule Organising Centre – MTOC); organise spindle fibre formation during cell division; involved in forming cilia/flagella.
  • 2. Interphase (S/G2): Centriole pair replicates (two centrosomes formed).
  • 3. Prophase: Centrosomes migrate to opposite poles.
  • 4. Spindle Formation: Microtubules grow from centrosomes to form the mitotic spindle.
  • 5. Chromosome Attachment & Separation: Spindle fibres attach to centromeres, align chromosomes (Metaphase), and separate sister chromatids (Anaphase).
  • 6. Centrioles directly pull chromatids apart.
Reason Incorrect (#6): Centrioles, as part of the centrosome, organize the mitotic spindle. The spindle microtubules attach to chromosomes and shorten, which pulls the sister chromatids apart during anaphase. The centrioles themselves do not directly pull the chromatids; they serve as organizing centers for the microtubules that do the pulling.

The rate of transpiration was measured for Helianthus annuus (sunflower) and Nerium oleander (oleander) under varying Leaf Vapour Pressure Deficit (LVPD) conditions (0 to 4.0 kPa). Based on typical responses (sunflower = mesophyte, oleander = xerophyte), compare the likely transpiration responses of these two species to increasing LVPD.

Click the INCORRECT comparative statement:
  • 1. Both start at/near 0 rate at 0 kPa LVPD.
  • 2. Both likely increase rate as LVPD increases initially.
  • 3. H. annuus (sunflower) likely has a consistently lower rate than N. oleander (oleander) (except potentially at 0 LVPD).
  • 4. H. annuus likely shows a steeper initial increase (more sensitive to moderate LVPD increases).
  • 5. H. annuus might plateau or decrease rate at high LVPD due to stomatal closure, while N. oleander’s rate, though lower overall, might be maintained better at high LVPD due to adaptations.
  • 6. A significant quantitative difference is expected, with H. annuus having a higher peak rate.
Reason Incorrect (#3): As a typical mesophyte, Helianthus annuus (sunflower) is expected to have a significantly higher rate of transpiration compared to Nerium oleander, a xerophyte adapted to conserve water, across most increasing LVPD conditions (before stress-induced stomatal closure might occur in the sunflower).

Nerium oleander is a xerophyte, adapted to dry conditions. Describe two distinct structural adaptations commonly found in its leaves that serve to minimize water loss via transpiration, and explain the mechanism by which each adaptation reduces the rate of water vapour diffusion from the leaf.

Click the statement describing a feature NOT typically considered a water-saving adaptation for a xerophyte like Oleander:
  • 1. Adaptation: Stomata located in sunken pits/crypts. Explanation: Traps humid air, reducing water potential gradient, lowers transpiration. Protects from wind.
  • 2. Adaptation: Thin, single-layered epidermis. Explanation: Allows rapid gas exchange but increases water loss.
  • 3. Adaptation: Hairs (trichomes) often present within stomatal pits. Explanation: Further traps moist air, reduces air movement, maintains humidity, lowering water potential gradient, reduces transpiration.
  • 4. Adaptation: Thick waxy cuticle on the epidermis. Explanation: Impermeable barrier reducing water loss directly through epidermal cells (cuticular transpiration).
Reason Incorrect (#2): Xerophytes like Nerium oleander possess adaptations to reduce water loss. A thin epidermis would facilitate water loss. Common adaptations include features like a thick cuticle or often a multi-layered epidermis (in Oleander), which increase the barrier to water diffusion, unlike a thin epidermis.

Explain how the specific sequence of amino acids in the variable regions of an antibody’s heavy and light chains leads to the formation of a unique three-dimensional antigen-binding site, conferring specificity for a particular epitope.

Click the INCORRECT statement regarding antibody specificity:
  • 1. Unique Amino Acid Sequence: Variable regions have unique primary structure (amino acid sequence).
  • 2. Specific 3D Shape: This amino acid sequence dictates the folding into a precise 3D tertiary/quaternary structure for the antigen-binding site.
  • 3. Non-Complementarity: This unique 3D shape is generally non-complementary to the specific shape of an antigen’s epitope, allowing broad binding.
Reason Incorrect (#3): The specificity of antibody binding arises precisely because the unique 3D shape of the antigen-binding site, determined by the amino acid sequence, is highly complementary to the shape of a specific antigen epitope (like a lock and key). This precise fit allows for high-affinity binding only to that specific epitope, conferring specificity, not broad binding to non-complementary shapes.

State the primary function attributed to the flexible hinge region present in many types of antibody molecules (such as IgG).

Click the INCORRECT statement about the hinge region’s function:
  • 1. Provides rigidity, holding the antigen-binding “arms” in a fixed position.
  • 2. Allows the two antigen-binding “arms” (Fab regions) to move relative to each other.
  • 3. Enables binding to antigens/epitopes spaced differently or located on curved surfaces.
Reason Incorrect (#1): The hinge region of an antibody provides flexibility, allowing the two Fab arms (which contain the antigen-binding sites) to move independently and adopt different angles. This enables the antibody to bind effectively to epitopes that may be spaced at variable distances on an antigen surface, rather than holding them rigidly fixed.

Explain the immunological advantage provided when antibodies, bound to a pathogen or antigen, also bind via their constant region to specific receptors present on the surface of phagocytic cells like macrophages (a process known as opsonisation).

Click the INCORRECT statement about opsonisation:
  • 1. This process (opsonisation) flags or tags the pathogen/complex for phagocytosis.
  • 2. It makes it much easier for the macrophage (phagocyte) to recognise, engulf, and destroy the antibody-coated target.
  • 3. It inhibits phagocytosis efficiency.
Reason Incorrect (#3): Opsonisation, the coating of a pathogen with antibodies (or complement proteins), significantly enhances the efficiency of phagocytosis. The binding of the antibody’s constant region (Fc region) to Fc receptors on phagocytes acts as a strong signal, facilitating recognition and engulfment of the pathogen, thus greatly increasing, not inhibiting, phagocytosis efficiency.

Describe the post-transcriptional process of alternative splicing as it occurs in differentiating B lymphocytes (plasma cells). Explain how this mechanism allows for the generation of a vast diversity of antibody variable regions from a finite number of immunoglobulin gene segments encoded in the genome. (Note: While V(D)J recombination is the primary driver of variable region diversity *before* transcription, alternative splicing can affect constant regions and membrane-bound vs secreted forms, but the question frames it regarding variable regions – interpret broadly or focus on the general splicing concept).

Click the INCORRECT statement about alternative splicing:
  • 1. After transcription, the primary RNA transcript contains coding regions (exons) and non-coding regions (introns).
  • 2. Intron Removal: Non-coding introns are spliced out (removed) from the primary transcript.
  • 3. Exon Recombination (Alternative Splicing): The remaining exons can be joined together in different combinations to produce different mature mRNA molecules.
  • 4. All potential exons present in the primary transcript must always be included in the final mature mRNA.
  • 5. This process allows a single gene (or pre-mRNA) to potentially code for multiple different protein isoforms (like different antibody forms or other proteins).
Reason Incorrect (#4): The core principle of alternative splicing is that different combinations of exons can be included or excluded from the final mature mRNA. It is not required that all potential exons be included in every mRNA molecule produced from that gene; the selective inclusion/exclusion of exons is what generates the diversity of mRNA (and thus protein) isoforms. (Note: V(D)J recombination, not splicing, is the main mechanism for *variable* region diversity).
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